[ in-fawr-muhl ]
/ ɪnˈfɔr məl /
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See synonyms for: informal / informally on Thesaurus.com

without formality or ceremony; casual: an informal visit.
not according to the prescribed, official, or customary way or manner; irregular; unofficial: informal proceedings.
suitable to or characteristic of casual and familiar, but educated, speech or writing.
Grammar. characterizing the second singular pronominal or verbal form, or its use, in certain languages: the informal[hasp] tu in French.
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Origin of informal

First recorded in 1595–1605; in-3 + formal1

synonym study for informal

3. See colloquial.

usage note for informal

The label Informal is used in this dictionary to mark terms that are not likely to occur in serious, prepared speech or carefully edited writing except when used intentionally to convey a casual tone. But under what circumstances is informal English apropos, appropriate, A-OK, even bitchen? What exactly is informal English? And how does it differ from slang, which is even more unlikely to occur in formal speech or edited writing?
Most sources agree that informal English typically avoids long, complex sentences, features a liberal use of contractions and other casual terms, and—in speech—allows elided pronunciations like gonna for going to . The particular words and phrases that dictionaries label Informal tend to be short, metaphorical, and somewhat out of place in carefully edited, serious prose. They include terms like abs, carbs, guys, big shot, spill the beans, and knock it off. Familiar, intimate, and unpretentious, in relaxed circumstances informal English is the frequent choice of a wide range of users, including educated speakers.
Dictionaries do not apply special labels to terms that occur in the most neutral variety of the language, which is so much the norm that we tend not to notice it. Nor do they label formal terms. Habitual users of English, however, are aware of different levels of formality. For example, in ordinary, neutral English we might say that people are worried or nervous. More formally, they are apprehensive, disquieted, or beset by misgivings. Informally, they may be antsy, in a lather, or spooked. And in slang, they can be uptight, wired, or bummed out. In the second sentence of this note, apropos is formal, appropriate is neutral, and A-OK is informal. At the other end of the linguistic spectrum from the formal apropos is the slang term bitchen, meaning “marvelous” or “wonderful.” In effect, informal English is English that is not quite neutral but not quite slang.
Slang is very informal, and its environment is often restricted, in that some of its terms are associated with a profession (military slang), a period of time (jazz-age slang), a group or subculture (teen slang), or an interest or activity (computer slang). Slang is characteristically metaphorical ( airhead for “a scatterbrained person”), playful ( canoodle for “to pet; fondle amorously”), elliptical ( bro for “brother”), vivid ( coffin nail for “a cigarette”), and ephemeral ( cat's pajamas, 1920s slang for “something wonderful”). Some slang is vulgar. Slang terms rarely occur in formal, prepared speech or in edited writing. Informal language, on the other hand, has recently seeped into situations that once mandated careful, formal speech. For some, this is a welcome development. But not everyone is pleased; complaints are sometimes heard when people think that a speaker in some relatively formal situation, trying to be folksy, has come across as insufficiently professional, professorial, or even presidential.
But although dictionaries categorize levels of linguistic formality on the basis of extensive observation of actual language use, the boundaries between these levels are flexible and porous. English as a widely spoken language is especially fluid and ever changing. Unlike some languages, it is not subject to dicta by a supervisory or regulating body. Throughout the history of English, some words in its lexicon have moved up from one category to another and then another—sometimes quickly, sometimes over centuries. The word snide, “nastily derogatory,” was once slang, as were tip, “a gratuity paid for service,” and frame, “to incriminate with false evidence.” In fact, slang terms that catch on broadly and firmly enough to remain in common use beyond one generation can generally be said to have outgrown their Slang label. Movement in the other direction, from neutral to slang, is far more rare. One classic example is bastard. Its literal sense, “a person born of unmarried parents,” first appeared in the late thirteenth century, almost two centuries before such an individual could be referred to as illegitimate. The current slang senses, “a despicable person” or just “a person” ( The poor bastard broke his leg ), did not emerge until the early to mid nineteenth century. Unlike words whose status moves from slang through informal to neutral, all the while retaining their original meanings, standard words that move the other way and become slang tend to do so by adding a new, usually metaphorical, sense.
Not all dictionaries agree when categorizing words and phrases on a sociolinguistic scale. These decisions are difficult to make. A word or definition labeled Slang in one dictionary but Informal in another may be unlabeled in a third. And yet, whatever guidance one finds in a reputable dictionary is usually sufficient. Most of us can judge when to vary our language. Consciously or unconsciously, we choose language appropriate to each communicative setting. And much of the time, a dash of informality is just … dandy.


in·for·mal·ly, adverbqua·si-in·for·mal, adjectivesu·per·in·for·mal, adjective
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023

How to use informal in a sentence

British Dictionary definitions for informal

/ (ɪnˈfɔːməl) /

not of a formal, official, or stiffly conventional naturean informal luncheon
appropriate to everyday life or useinformal clothes
denoting or characterized by idiom, vocabulary, etc, appropriate to everyday conversational language rather than to formal written language
denoting a second-person pronoun in some languages used when the addressee is regarded as a friend or social inferiorIn French the pronoun "tu" is informal, while "vous" is formal

Derived forms of informal

informally, adverb
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012